The military has a need for low profile, low cost, low maintenance antennas that can be flush mounted on various types of land, air, and water platforms, including but not limited to tanks, aircraft, ships, and even articles of clothing. Low profile phased arrays are currently offered by the aircraft industry. Low profile mechanical scanned antennas, which provide wider scan coverage at a much lower cost, are also available. Phased arrays and mechanical antennas are each suited to the requirements of different platforms. Both of these are considered surface mounted low profile antennas.
Although using the aircraft structure as an actual part of the radiating antenna is very attractive, most of the time it is impractical. Combining antenna installation and platform manufacture may simplify the fabrication process and reduce cost; however, the materials and shape of the aircraft may not be compatible with antenna design requirements.
Microstrip patch antennas have also been proposed. Examples of microstrip antennas are U.S. Pat. No. 4,812,853 (Negev), U.S. Pat. No. 5,008,681 (Cavallaro et al.), and U.S. Pat. No. 5,355,142 (Marshall et al.). However, a microstrip patch antenna is less efficient at VHF/UHF. Also, microstrip antennas are inherently narrowband (only a few percent), making them unsuitable for most VHF/UHF communication applications. In general, to be an efficient radiator an antenna must be resonant. Thus its size must be close to one-half the operating wavelength. At VHF/UHF this can be several meters to several tenths of a meter. Because of limited real estate on platforms such as aircraft, microstrip patch antennas are seldom used below 1 GHz.
In summary, patch antennas for frequencies below 1 GHz have very limited application in airborne systems. For those applications that do exist, antennas made using existing technology can be flush mounted on existing aircraft platform. Integrating them into the aircraft structure (so that they are part of the airborne platform) is technically very difficult, and does not offer any better performance or cost benefits.
In the microwave and EHF bands, microstrip antennas offer great benefits. They are thin, light weight, and low profile, and their 5 to 10% bandwidth is sufficient for most COM and RADAR applications. Bandwidth can be further increased by adding another dielectric layer with a passive patch on top of it. Furthermore individual patches can be networked into a group of radiating elements resulting in well-known, phased-array antennas. Phased arrays of microstrip patches offers superior performance, such as high gain, electronic steering, independent multiple beams, frequency agility, adaptive pattern control, digital beamforming, etc. Although patches appear simple in design, they require specific substrate materials in precise physical structures that typically consist of multi-layer boards. However, conventional, flat panel PC board technology cannot be applied on sharply or double curved aircraft surfaces such as aircraft wings, aircraft body, etc.
It is to the solution of these and other objects to which the present invention is directed.